When do you need to whitelist an email manually?
When your email server automatically blocks an email from a verified sender.
How to whitelist an email?
Login to your cPanel, go to (Email) – (Spam Filters)

Then select (Show Additional Configurations) – (Edit Spam Whitelist Settings)

Whitelisting email addresses should be inserted as follows:
- user@company.com — To whitelist a single email address.
- *@company.com — To whitelist all of the addresses at company.com.
- ?ser@company.com — To whitelist a single character in an address at company.com (i.e., user@company.com, but not theuser@company.com).